Generally, the term “Moving Picture Experts Group (MPEG)” refers to a standard technology for moving pictures, and is a method in which a transmitter compresses and transmits moving pictures and a receiver decodes and reproduces them.
The operation of MPEG is briefly described below. First, an encoding and transmitting side digitizes given video and audio signals, compresses two types of signals through an encoding step of compressing them with minimized loss, multiplexes the two types of signals into a single bit stream, and outputs it.
The data converted into the bit stream as described above may be stored in a medium, or be transmitted via a wired or wireless connection and transferred to a receiving side. The receiving side, which reproduces it, performs the reverse process of separating signals using a multiplexer, decoding the signals through a decoder and reproducing the signals on the multiplexed bit stream data.
One of the important technologies in the above-described procedure is that the video signals and the audio signals, which are simultaneously generated and acquired and are then converted into a bit stream, are reproduced by the receiving side in a state in which the video and audio signals are closely synchronized with each other. In this case, the synchronization between the video and audio signals means that the picture and sound are synchronized at the time of being reproduced.
A conventional method for the synchronization of digital video signals and digital audio signals which has been used until now is a method of recording time information (a Decoding Time Stamp; hereinafter referred to as a DTS) which must be decoded in respective video data and audio data and/or time information (a Presentation Time stamp; hereinafter referred to as a PTS) which must be reproduced in a header of unit data (hereinafter, a data unit in which time information can be recorded is referred to as a “frame”), multiplexing the time information and, thus, learning reproduction time and performing reproduction based on the time information at the time of reproduction.
The method of recording the time information is described in detail below. When encoding is completed on a frame basis, a time point at which the encoding of one frame begins or a time point at which encoding is completed is measured and set for a reference time (hereinafter referred to as a ‘reference clock’), a DTS or PTS is acquired through calculation assuming that the same frame rate is applied based on the reference clock, the DST or PTS is recorded at the time of multiplexing, and then conversion into a bit stream is performed. In the case of MPEG 4, a Composition Time Stamp (CTS) functions as the PTS.
However, the conventional synchronization method still has several problems in spite of its various accurate constructions.
Of the problems, the biggest one is that synchronization is still not perfect. One significant reason why a problem is caused in the synchronization itself is that the rate at which the Central Processing Unit (CPU) of an encoding device processes frames is not uniform because a low performance input device or a low performance reproduction device is used. If the reference clock is captured as the time of the encoding step when encoding is performed in low performance hardware, the DTS or PTS provided through calculation based on the reference clock is calculated according to a uniform criterion on the assumption that the performance of the encoding device ensures a uniform frame rate. However, a low performance encoding device cannot process data at a uniform frame rate due to the load on itself. That is, the actual DTS or PTS is different from the calculated DTS or CTS. Accordingly, if an erroneous PTS or CTS is used when video signals and audio signals are not uniformly processed, a synchronization problem occurs.
In another case, a phenomenon in which some of the video signals and audio signals of a bit stream to be reproduced are omitted occurs. In this case, some data are not reproduced at the time of reproduction, so that a phenomenon in which audio data is not synchronized with video data, that is, pictures do not match sounds, occurs.
Recently, with the development of technology, the amount of data to be transmitted and processed has dramatically increased, so that synchronization has gradually become an issue. Furthermore, as digital broadcasting has been provided in practice, unsynchronized reproduction in digital broadcasting is inconvenient to customers and, at the same time, has a bad effect on the reputation of a data transmitter.
As a result, an improved data processing method and system capable of decreasing poorly synchronized reproduction are strongly required.